A Global Positioning System (GPS) is a space based global navigation satellite system that utilizes a network of geo-synchronous satellites which may be utilized by a GPS receiver to determine its location. Many telematics systems incorporate a Global Positioning System (GPS) receiver, which can be used to obtain the location of a vehicle at a certain measured time. By comparing the location of a vehicle at a plurality of measured times, the speed of the vehicle may be determined. GPS receivers can also determine speed by measuring the Doppler shift in the received satellite signals. The acceleration of the vehicle may be determined as the change in speed divided by the time between the measurements. A GPS receiver's ability to determine acceleration can be limited due to the dependence of the measurement upon factors such as reception and satellite availability. In addition to location information, a GPS receiver may also be configured to provide time data.
An accelerometer is a device that measures acceleration associated with the weight experienced by a test mass in the frame of reference of the accelerometer device. The acceleration measured by an accelerometer is typically a weight per unit of test mass, or g-force.